Modern microprocessors and microcontrollers include circuitry that efficiently allows analyzing a running program by means of a so-called in-circuit debugger or emulator device. To this end, a microcontroller or microprocessor provides for internal circuitry that supports debugging functions and a specific interface which can be for example activated by programming multiple function pins of the device to operate as the debug interface. Such an interface usually can be configured as a high speed serial interface to allow for fast communication between the actual device and the external debugger or emulator. The device itself can thus be operated in a normal operating mode which does not activate this interface and associated pins can be used for other purposes and a debug operating mode which uses this interface to exchange data with respective external devices, such as debuggers or emulators that can be operated from and by an external host computer. The debuggers or emulators can also be operated as programmers, wherein the program is transferred into the target device via the same debug interface. Host computer, external debugger or emulator thus forms an inexpensive analysis and debugging system.
Modern processors and microcontrollers provide for an extended set of debug functions inside the respective device. For example, a number of breakpoints can be set within the device to allow the device to actually run in real time which would not be possible with an external debugger when using just a high speed serial interface and thus would require bond-out chips and expensive debug circuitry. However, the functionality of these internal debug circuitries is of course somewhat limited due to a limited amount of silicon real estate and other reasons. For example, trace back functions are often not supported by external in circuit debuggers and even more complex in circuit emulators may not sufficiently support a trace function when in debug mode, in particular when the device executes a reset.